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bovhica

Tow vehicle and trailer light troubleshoot

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bovhica

Hey Crew, 

I'm stumped maybe someone can help.  I haven't towed our boat with my wife's rig before.  I've only towed it with mine and all trailer lights work fine.  I hooked it up to my wife's hitch and plug because we are planning on towing it with her vehicle next weekend for a camping trip.  Unfortunatly after I hooked up there were no running lights, no brake lights, and no signal lights, however the tail lights illuminate with or without her headlights on?  I checked the fuses and they were good. I also used a circuit tester and clamped to the ground pin on the vehicles plug and tested the running light and blinker pins.  All pins tested and working.  I reconnected trailer to my truck just to check that the problem wasn't in the trailer and confirmed that all lights are operational.  Any ideas?

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Eagleboy99

Are the pinouts the same hers to yours?

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shadetreefab

Are we talking flat 4/5 or round 7 pin?

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bovhica
1 minute ago, Eagleboy99 said:

Are the pinouts the same hers to yours?

Yes.  Same 7 way plug using only 4 pins on boat trailer. Running lights, blinkers and ground in same position on both vehicles.

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bovhica
2 minutes ago, shadetreefab said:

Are we talking flat 4/5 or round 7 pin?

7 round both vehicles and trailer.  However trailer plug only using 4 pins.  Running lights, ground and blinkers left and right.  

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oldjeep

Have you had her vehicle attached to any other trailer and had it work?  Ford used to do a stupid thing where they prewired the truck, but didn't install a couple fuses and relays to actually make the trailer lights work - could be something like that.

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shadetreefab

If using the same adapter, insert plug and hold it by the ears, then rotate it slightly back and forth like an 1/8 of an inch, do this with your hazards on.

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Eagleboy99
4 minutes ago, bovhica said:

7 round both vehicles and trailer.  However trailer plug only using 4 pins.  Running lights, ground and blinkers left and right.  

Brakes?  https://en.wikipedia.org/wiki/Trailer_connectors_in_North_America  Note two variants of SAE J560 plug.  If everything else checks out then it must be IN her vehicle.

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bovhica
2 minutes ago, oldjeep said:

Have you had her vehicle attached to any other trailer and had it work?  Ford used to do a stupid thing where they prewired the truck, but didn't install a couple fuses and relays to actually make the trailer lights work - could be something like that.

I have not used it before for towing.  Didn't ever have the need.  It's a Mercedes GL 450

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Eagleboy99

One other thing to check...  corrosion in her truck's plug - I had this isse with mine.  Those plugs are generally craptastic quality (is there an adapter in the the line?)

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bovhica
1 minute ago, shadetreefab said:

If using the same adapter, insert plug and hold it by the ears, then rotate it slightly back and forth like an 1/8 of an inch, do this with your hazards on.

I'll give thos a shot....thanks.

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Eagleboy99

Time to break out the DVM!  :)

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Ballay

Do you have a volt meter?

On the 4 pin, naked pin is ground then tail lights then left turn signal/ brake lights and right turn signal/ brake lights. 

Ground to lights 12volts with lights on

ground to left or right, 12 volts with brakes pressed or temporary with blinker. 

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Eagleboy99

Or a 12v bulb and a couple pieces of wire.

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bovhica
7 minutes ago, Eagleboy99 said:

One other thing to check...  corrosion in her truck's plug - I had this isse with mine.  Those plugs are generally craptastic quality (is there an adapter in the the line?)

No corrosion from visual inspection.  Looks like it's in a lot better shape than mine...lol.  it's a factory install and no adapter in line that I can see.  I'm at a loss!

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bovhica
5 minutes ago, Ballay said:

Do you have a volt meter?

On the 4 pin, naked pin is ground then tail lights then left turn signal/ brake lights and right turn signal/ brake lights. 

Ground to lights 12volts with lights on

ground to left or right, 12 volts with brakes pressed or temporary with blinker. 

I don't.  Probably have to pick one up or just take the vehicle to a professional...lol. Just to clarify I'm using 7way round but there are only 4 pins being used on trailer plug, the other slots are bare.

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Eagleboy99
Just now, bovhica said:

I don't.  Probably have to pick one up or just take the vehicle to a professional...lol. Just to clarify I'm using 7way round but there are only 4 pins being used on trailer plug, the other slots are bare.

You can get a DVM for a few bucks at Harbor Freight etc.  Worth every penny.  Or the lightbulb trick.  You need to see if ther eis even voltage at the pins.  BTW, I use the same 7-4 adapter on mine.

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gregtay

I know for my Audi and VWs I needed a special 7 pin adapter that worked with the computer to detect the trailer. These German cars need to know the trailer is there to go into trailer mode and I think the LED lights on the trailer don’t have enough resistance. Not sure if Mb is the same way but I wouldn’t be surprised. Without the special adapter the lights didn’t work.

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gregtay
1 minute ago, gregtay said:

I know for my Audi and VWs I needed a special 7 pin adapter that worked with the computer to detect the trailer. These German cars need to know the trailer is there to go into trailer mode and I think the LED lights on the trailer don’t have enough resistance. Not sure if Mb is the same way but I wouldn’t be surprised. Without the special adapter the lights didn’t work.

Something like this: https://www.uhaul.com/MovingSupplies/Wiring-Lights/Adapters/LED-Light-Trailer-Module/?id=4089

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bovhica
Posted (edited)

So I just did a volt meter test.  The GL 450 has 13.2 steady volts to each signal whether signal is on or off and running lights has 3.8 volts with headlights on and off?  On a side note, center pin (reverse lights) has 3.5 volts with vehicle in park.

F250 has same voltage (13.2) to signals but only when signal is engaged and volts go up and down, like they should, with signal. 14.1 volts to running lights when headlights are on.  Both tests were done with engines at idle.  What does this tell you electrical guys?

Edited by bovhica

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bovhica
6 minutes ago, Ballay said:

Weird. A bad relay?

this has the pinout for the plug: https://www.ajtnt.com/7-way-rv-plug-diagram/

Not sure. I ordered an adapter for the GL.  Apparently the vehicle is programmed for filliment type bulbs and their resistance?  I know its wishful thinking to think the adapter will solve the problem considering my testing results but if that doesn't work it's going into the dealer.  I dont have the time, knowledge or patience for electrical troubleshooting.  Thanks for all the help!

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